Current limiting reactors which may be serially or shunt connected in power transmission or distribution systems or the like are, of course, well known in the art and numerous designs have been suggested to reduce as much as possible objectionable losses and heating effects due to eddy currents and the like. Current sharing between the various plural parallel conductors in inductive devices is a problem which, unless solved, results in unequal ac impedance between conductors with the result that most of the current flows through the conductor having the lowest impedance causing excessive heating thereof and possible overload or burnout. Current sharing may be achieved by a technique known as transposition, but transposed conductor inductive devices are difficult to design mechanically and electrically because of their complex geometric configuration and are difficult to manufacture. More recently reactors have been designed which eliminate the need to transpose the conductors, and attention is directed to U.S. Pat. No. 3,264,590 issued Aug. 2, 1966 to Anthony B. Trench, and assigned to the assignee of the present invention, and which describes a reactor utilizing a plurality of helically wound, coaxially disposed coils connected in parallel and having relative lengths and cross-sectional areas such that the induced emf across each coil is substantially equal. The coils connected in parallel are wound concentrically about a common axis. For various reasons it is frequently necessary for the different coils to be terminated at different points around the periphery of the common axis. To connect the coils together in parallel relationship and to the external circuit, a connector in the form of a spider having a plurality of arms extending radially from the common coil axis is provided at each end of the coil structure. The end of each coil is connected to the spider arm to which it is closest by conductors extending parallel with the axis of the coil. The spider is fabricated from aluminum sheet or bar stock material and is designed to perform three main functions, as follows. Firstly, the spiders provide a means of obtaining partial turns in order to force the currents in the various layers and packages forming the reactor to be balanced, as outlined above. For example, if the spiders have eight arms, and it must be emphasized that the number of arms is strictly a matter of design choice, it is possible to wind a layer having a number of turns equal to an integral multiple of one eighth turn. Secondly, the two spider system provides a means of grading the voltage across the coil. All conductors in any selected layer experience the same total voltage across them, but there is a voltage between adjacent conductors of the layer equal to exactly ##EQU1## of the voltage per turn (where n is the number of conductors high in the turn in the axial direction). This is because each conductor is terminated on a different spider arm. Assuming that there are N turns in the layer, then the total voltage across the layer is distributed over (nN) conductors instead of N conductors which would be the case if one conductor per layer had been used. Thirdly, all packages of the reactor are rigidly held between the two spiders by means, for example, of resin-impregnated glass fibre ties. The two spiders thus act as main structural members which contribute significantly to the overall strength of the reactor and provide means for lifting and mounting the reactor easily. The structural requirements of the spiders and the electrical, i.e., low loss, requirements are, however, frequently incompatible. The spiders contribute to overall coil losses in two ways (a) the I.sup.2 R loss due to the conduction current carried by the spider arms as they carry current to and from the packages, and (b) the eddy losses induced in the spider arms and hubs by the time rate of change of the main magnetic field of the reactor.
Considerable attention is being directed to the production of more efficient electrical inductive equipment and it is therefore of primary concern to reduce losses as much as possible. It has now been determined that one area in which reactor losses may be reduced is in the spider arms themselves.